Recently, in the field of material processing, laser processing has been generally spread widely as one of the processing techniques. For example, it has been recognized that laser welding and laser cutting provide higher processing quality as compared with other techniques. Market demands further high quality and high speed processing and also demands a laser oscillation apparatus and a laser amplifying apparatus which generates and emits a single mode laser light having a high output property, high efficiency, and a high light-collecting property, that is, having good beam quality (high beam quality).
In a conventional laser oscillation apparatus, a fiber in which a laser medium is added for realizing high output and a fiber for transmitting excitation light are disposed in adjacent to each other, and between the fibers, a material having a predetermined refractive index is filled. Such a conventional technology is described in, for example, Japanese Patent Unexamined Application No. 59-114883 and U.S. Patent Application Publication No. 4938561.
FIG. 8A shows a conventional laser oscillation apparatus. Laser oscillation apparatus 100 includes excitation light amplifying fiber 101 for transmitting excitation light, laser light amplifying fiber 102 containing a laser medium and coupling chamber 103. Excitation light amplifying fiber 101 and laser light amplifying fiber 102 are disposed in adjacent to each other. Coupling chamber 103 includes excitation light amplifying fiber 101 and laser light amplifying fiber 102 and is filled with a material having a predetermined refractive index.
FIG. 8B is a sectional view taken along line 8B-8B of FIG. 8A.
On both ends of laser light amplifying fiber 102, a final-stage mirror (not shown) for reflecting laser light and an output mirror (not shown) for taking out a part of laser light and reflecting the rest of the laser light are disposed. By the effect of these mirrors, laser light undergoes multiple feedback amplification.
Then, the operation of laser oscillation apparatus 100 is described. Excitation light propagating in excitation light amplifying fiber 101 enters laser light amplifying fiber 102 to excite the laser medium in coupling chamber 103. With the excitation and multiple feedback amplification, laser light is generated and emitted.
However, when high output is intended to be obtained in conventional laser oscillation apparatus 100, an excitation source is a high-output semiconductor laser, and the diameter of the excitation light amplifying fiber 101 is increased to be as large as about 100 μm. Therefore, for achieving high output, in order to allow the excitation light to enter the laser medium efficiently, the diameter of laser light amplifying fiber 102 is desirably equal to or larger than the diameter of excitation light amplifying fiber 101. However, in such a case, the beam quality is deteriorated.
On the other hand, to obtain laser light having good beam quality (high beam quality laser light), the diameter of laser light amplifying fiber 102 must be small. In general, in a case of near infrared laser light used for laser processing, for obtaining a high quality single mode laser light having good beam quality, the diameter of the laser light amplifying fiber must be about 6 μm to about 10 μm. Therefore, a conventional laser oscillation apparatus has a problem that high output and high beam quality laser light cannot be obtained.
The present invention provides a light amplifying fiber and a light amplifying method capable of obtaining high output and high beam quality laser light and realizing a small size and high efficiency.